Extensometer for testing metal objects



Sept. 8, 1953 R. H. PINKEL EXTENSOMETER FOR TESTING METAL OBJECTS 2 Sheets-Sheet 1 Filed July 15, 1949 mowwszw;

Sept. 8, 1953 R. H. PINKEL 2,651,196

EXTENSOMETER FOR TESTING METAL OBJECTS Filed July 15, 1949 2 Sheets-Sheet 2 dz/e 72%? @Zerf 34 25 P Ea. I

Patented Sept. 8, 19 53 i v UNITED STATES PATENT OFFICE EXTENSOMETER FOR, TESTING METAL OBJECTS Robert H. Pinkel, Chicago, Ill. Application July 15, 1949, Serial No. 104,929 4 Claims. (01. 73-885) The present invention relates to a testing device by an electrically actuated strain recorder that for testing the mechanical properties of bolts and would also provide an autographic record or diaother like objects. More specifically the invengram.

tion relates to an improved extensometer which The disadvantages with this latter type of test is especially adapted for determining the yield unit are also quite obvious. The measurement strength and elongation of metal test specimens. taken would be the function of many components In the development of metal parts such as bolts such as the grips, the bolt threads, etc. In addimine their relative strength qualities. Elonga- I the operation of the testing machine the grips tion and yield strength must in most instances normally may become misaligned. This causes be accurately and carefully determined in order an adverse efiect on the extensometer and results that proper comparisons may be made between in a false reading on the autographic record. A

a conventional test press and thus the material skilled in the art. After the modulus line has The point at which the metal yields in the final offset line is drawn parallel to the straightest maximum elongation is a factor which must be portion of the modulus line. The ofiset line is determined by such a test procedure. spaced from the modulus line and runs in parallel In the past, several difierent types of testing relation with respect thereto. The dimensional devices have been utilized, none of which have measurement of the offset line from the modulus succeeded in providing the industry with an acculine iS 0f the length of the p c men (exclurate and positive testing procedure. SiVe of pping surfaces) which is to be elon- The first of these would be the utilization of a gated. As the test specimen yields a load extenrecorder drum which would be connected by pul- 30 sion curve is formed tangent to the modulus line. leys and cables to the testing apparatus. Thus The point of intersection of the offset line With tain strength characteristics of the test specimen. From this description then of the e p ce- An' autographic load extension could be obtained dllre it is ly p t hat the modulus line by this method but it would have inherent weakmilsii be a St a ht as p b in Order to deterinaccurate readings, Th a ou t of extension 40 ofiset line measurement is to be taken. With a "acteristics, the autographic recording by a strain recorder.

Another device previously utilized is a type of It is another object to pr vi n mpr v d extensometer. This extensometer is usually atin d i h w ll ur ly per tached to the grips of a testing machine. The wi h a train grips upon moving would cause reaction in the y d a d ultimate S h of a metal Object extensometer. The reaction would be measured Such as a el i undercut portions 15 A still further object is to provide an extensometer that is readily adapted to be connected to the opposite ends of a test specimen to be measured and whereby the elongation of the test specimen and any changes in the characteristics of the metal will be directly imparted to the extensometer.

Another object is to provide an improved gripping arrangement for a testing device such as an extensometer.

These and other objects will become more clearly apparent from a reading of the description when examined in connetion with the ac-' companying sheets of drawings.

In the drawings:

Fig. 1 is a side elevational view showing a test unit and an extensometer.

Fig. 2 is a detail elevational view partiallyin section showing the relation of an extensometer with respect toatestspecimen, I f I Fig. 3 isa detail elevational view of a mounting support for an extensometer.

, Fig. 4 is a diagram shovv ing a typical autographic recording resulting of the applicants extensometer t when used in connection with a conventional type of strain recorder. p

t A testing device is reference character Fig. 1. The testing device includes a pair longitudinally spaced grips J, I, p The grips H may be of conventional construction, a u shaped hanger type generally being preferred. The grips i I are connected longitudinally aligned relation by means of bolts l2 to the platens iii of a testing machine. The testing machine has not beendisclosed since any conventional apparatus can be utilized that willexact the sufficient pressure for properly testing the elongation of the test specimen t I The grips ii also include gripping surfaces 14. The rippi ews c .1 a l i ud l spaced with respect to .each other and include The undercut portion l 5 9i each grip Jl terminates in a tapered bore lB. Aconicai insert ,1] is arranged to be secured it h gr n. .A

w h the tape e v er. I threaded bore 18 is iormedin one oi the inserts designated by the it as specifically shown in is provided with a plain bore lethrough which he shank qfa o .0 es 9 Jen A. i exd. he. b t A.v nc udesiheusu ead n the lower end of the poltis threaded so that it may be secured into the threaded bore N3 of the insert x As best indicated in Fig. 2 the bolt A is thus e r y n c ed. t. .thes ps- H and p longitudinal movement of the grips]! in a direction away from each otherthe bolt A would be placed under tensionandthus eventual elongation would result during thepperation of the testing press. The movegnent of the grips H in a direction away from each other is oi courseet a very slow rate til fracture of the metal bolt occurs v n An extensometer is'positioned adiacent to the grips H. This extenso'rneteris generally designated by the reference character '20 and includes a support 2!. Thelsupportif I may be rigidly secured to any'suitablesupportadjacent'the testing press. The ext ensoineter includes a pair of longitudinally"extending arms 22. The arms22 3- ,A 1.9

are'freely pivoted as indicated at of track rnembers" 24'extend vertically in lateralr ly spaced relation forming a track 25. An up- 6 s bs t nd q ins ie. he o h i ser and thepressure is constant unper sliding block 26 is adapted to be moved verticaliy within the track 25. The sliding block 26 includes a contact projection 21 which extends outwardly of the block. A screw and nut 28 pivotally secure the block 26 to the upper arm 22. A lower block 29 is also positioned within the track 25 and is adapted to move therein. The lower block29 is pivotally secured in a similar manner as the block 2% to tlie lower arm 22 as indicated at 30. A current control device 31 is rigidly supported by the lower arm 22. The current control device 3! includes a plunger 32. electrical ccinduit 33 is suitably connected to terminals on the current control device 3!. This current control device 31 is of the pressure-responsivetypa In other words, as the upper and lower arms 22 pivot in a direction apart, the plunger 32, which is spring controlled, is urged outwardly against electrical changes occur within the current control evice. Likewise whe'n the arms 22 move toward each other during the setting up been: tion oi the extensorneter, the projection 21 engages the plunger '32 and movesthe same. The device '31 is usually connected to a conventional type of electrically operated strain recorder not shown. The type of strain recorder utilized is capable of making an 'a'uto gr'aphic load extension diagram in a well known manner thus producing a modulus line in response to the mechanical action or theextensonieter. Afset screw 3'4 is positidned to retain the block 29 in the track 25. w The -extens'orneter is also provided with a contact extension 35 which is secured'to the end of the upper arm 22. The contact extension 35 includes a longitudinally extending piece which is provided with slots 36. Bolts 31 are connected through the slots 38 and may be loosened and tightened for effecting longitudinal adjustment of the contact extension 35 with respect to the upper arm 22. The eomaerextension 35 includes 'a'contact member. 38. The contact member 38 extends substantially perpendicular with respect to the extension 3 5. 'rneeohtsa member '38 is tapered and terminates in 'a 'rounded'or pointed contactjend which ma have point to 'pomtnga'geiri'ent'with' a test 's'pecimeri n'a masne'r'wmeh will presentlybe'rrio're app-area 7 Anadjus'tingplate 39 is 'rigidly secured to the end of the lower'arin '22. The adjusting'piatefl includes a piurauty'or spaced vertically extendingslots' ifl. A contact extension fil is'securedto the adjusting plate at. The contact extension Al also includes a contact member l 2 which is the same 'manner as the rounded or pointed in contact rnembezr 158. The contact members 38 and 42 are positioned so that they point toward each other and they are ormally' placed in longitudinal align nent when they are connected to the opposite ends of a test specimen as indicated in Figs. l and 2. The extension; 4l *alsodncludes a plurality of spaced slots 43. Bolts 44 extend through the slots 43 for rigidly securing the-ex;- tension to the adjusting plate 39, The bolts may be loosened o r ;per nitting lateral adjustent of the extension. A spring 45, as shown in F1 g. 1, is provided for nqrmallyurging the arms 22 in a lateral direction toward one another.

As best shown in Figs. 1 and 2, tliecontact members 38 and 42 are positioned in substantialiy longitudi alalignment. The contact ends of the contact members engage opposite ends of'the test specimen or bolt A;pin point to point relation, Thespring 45 tends to urge the contact members 33 "and 42 him this position. It is especially important that the contact members be accurately aligned and for this purpose adjustment of the extensions 35 and 4| is possible.

prior to this fracture failure for the reason that the extensometer might be injured by the sudden shock as the grips came apart. Since the exmachine moves the grips H apart, any l ngation elongation is possible. It can readily be seen now tact points 38 and 42 which also thus are spread apart. This movement results in pivotal movements of the arms 22 in a direction awayzfrom each other. The plunger 32 may be spring biased With the utilization of this novel extensometer 'of a conventional type of strain recorder.- It mate tensile strength of a test specimen may be this application. Applicants invention is exemplidisclosed nor the scope thereof as defined in the is imparted to the arms 22, this movement in turn the grips, the grips being relatively movable for which is a disadvantage found in the previous t t end of one t t member facing th zontal indices or mark n s express total elongaand the arms are moved in direct response to the Fig. 4, the modulus line is shown as extending in a substantially straight line. This is accompl d y pp novel extensometer Whereand a specimen to be tested, current control means grips is not a vital factor or force causing ir- 2. For a testing device for bolts and the like extension curve indicates the point O yield as grips, said extensometer including a supporting drawn from the end of the load extension curve on t supporting b means n one of the plicants I'm/811131011- In P s m te rection with respect to the first arm, a second place in the test specimen, since the extensometer would have to be disconnected from the machine relation whereby changes in the length of the test specimen in response to mvem' ent of Isa-id grips imparts relative movement to tontact membars.

3. *For a testing device for bolts and the like having a pair of testing gripseaeh grip mcluding a gripping surface, the grips being relatively movable whereby the gripping surfaces are movablein -a longitudinal direction other, each gripping surface .including an'opening, the openings being in substantially axial adjustment, and an insert secured in 'each opening, eaoh -msert being arranged and constructed to secure a test specimen between the igripping surfaces 'of the grips; an Leatensometer positioned adjacent the grips, said extensometer including a supporting member, first and second arms pivotally supported on the supporting member, the arms extending in a direction toward the gr ins, said arms shaving end portions movable lateralli away iro'm each other, a pressure responsive current control device on one of said arms, :means on the other arm actuating the current control device during respective lateral movement of said arms, a contact extension "connected :to the first arm, said contact extension being relatively adjustable in a longitudinal direction with respect to the first arm, an adjusting .plate carried by the second arm, a second contact extension car- =ried-on said adjusting plate, means connecting said second contact extension to said addnsting plate to provide for relative 'lateral-and-longitudi- *n'al adjustment of the second contact extension with respect to the second arm, and -a pointed contact -member on each'contact extension, each contact member being arranged to engage -oppo- I site ends-oi a test-specimenin-aa-dally-alignedpinpoint relation whereby changes in the length of the test specimen in response to movement of said grips imparts relative movement tosaid con- 'tact'members.

4. For a testing device for bolts and the dike, the device havinga pair'of testing grips adapted portions :of a test specimen, the movable longitudmally away irom each other; extensometer positioned adjacent the grips, said extensometer including a supporting member, first and second arms pivotallv supported on-saidsupporting member, s'aid zfirst -and second arms having end portions moraine laterally toward and away from each =other, a current control device carried by said supportim; member adjacent said arms, means on one or said arms for actuating the control device during movement of one of said arms, a first contact member 'on the first arm, saidifirst contact-member extending laterally toward the sec'on'd'arm, :a contact e tension, means adiustably connecting :said c'ontaot extension to said second arm whereby said 'contaot extension may bemoved longitudinally with respect to :said second arm, a second contact member on the contact extension, said second contact member extending laterally ctowardthe first contact mem- .'ber, the iconta'ot members being arranged to engage opposite ends or a test specimen .in axially aligned relation whereby changes in the length or a test specimen in response to movement of said gripsimparts relative :movement to said contact members.

to n e sp ced grips being relatively RGBERT H. PINKEL.

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